The present invention relates generally to improved precision manufactured web, web guide members made by an improved precision manufacturing process. One embodiment of the improved manufacturing process and improved web guide members is described in relation to precision backer bars for use in electrostatographic printing systems for controlling tension and tolerances of a moving web.
Rounded web guide members are used frequently during many processes for handling or manufacturing moving webs. Examples include photographic film and paper manufacturing, paper manufacturing, rolled steel and aluminum manufacturing and any number of similar operations. Rounded web guide members are often used in such applications to provide support, tension, and directional control of the moving web. The more precise the requirements for uniform treatment of the web, the more precise the requirements for uniform straightness and curvature of the rounded web guide members.
One embodiment of an apparatus requiring extreme straightness and length-wise uniformity of web guide members occurs when such web guide members are used as backer bars within imaging-web based electrostatographic printing systems. Backer bars are commonly used in such electrostatographic printing systems to hold flexible electrostatographic imaging members in proper position with proper tension. In order to understand the function and importance of backer bars, a description of printing systems utilizing flexible imaging members follows:
Flexible electrostatographic imaging members are well known in the art. Typical electrostatographic imaging members include, for example, photoreceptors for electrophotographic imaging systems and electroreceptor such as, ionographic imaging members for electrographic imaging systems. These imaging members generally comprise at least a supporting substrate layer and at least one imaging layer comprising thermoplastic polymer matrix material. The xe2x80x9cimaging layerxe2x80x9d as employed herein is defined as the dielectric imaging layer of an electroreceptor or the photoconductive imaging layer of a photoreceptor. In a photoreceptor, the photoconductive imaging layer may comprise only a single photoconductive layer or a plurality of layers such as, a combination of a charge-generating layer and a charge transport layer.
Generally, in the art of electrophotography, the process of electrophotographic printing or copying is initiated by exposing an analog or digitally created image of an original document onto a substantially uniformly charged photoreceptive member. Exposing the charged photoreceptive member to a light image discharges a photoconductive surface thereon in areas corresponding to non-image areas in the original document while maintaining the charge in image areas, thereby creating an electrostatic latent image of the original document on the photoreceptive member. This latent image is subsequently developed into a visible image by depositing charged developing material onto the photoreceptive member surface such that the developing material is attracted to the charged image areas on the photoconductive surface. Thereafter, the developing material is transferred from the photoreceptive member to a receiving copy sheet or to some other image support substrate, to create an image, which may be permanently affixed to the image support substrate, thereby providing an electrophotographic reproduction of the original document. In a final step in the process, the photoconductive surface of the photoreceptive member is cleaned with a cleaning device, such as, elastomeric cleaning blade, to remove any residual developing material, which may be remaining on the surface thereof in preparation for successive imaging cycles. Electrostatographic copying and printing processes similar to those described above are well known. Analogous processes exist in other electrostatographic printing applications such as, for example, ionographic printing and reproduction where charge is deposited on a charge retentive surface in response to electronically generated or stored images.
An exemplary use of backer bars in such systems is described in U.S. Pat. No. 5,708,924, issued to Shogren et al. and hereby incorporated herein by reference. The backer bars in Shogren are mounted within a customer replaceable unit that includes a corner and support structure for supporting a photoreceptor belt while it is packaged, shipped and inserted over drive and idler rolls in a machine. The customer replaceable unit prevents a machine operator from having to handle the belt itself and provides protection from extrinsic damage. The system as described includes web guide members for tensioning the photoreceptor belt during use.
Throughout the electrostatographic imaging process described above, the photoreceptor web must be held in positions within tight tolerances. As shown and described in Shogren, many of these tolerances are maintained by web guide members such as, backer bars. Because of the requirements for tight tolerances, precision manufacturing of prior art backer bars has been an expensive and work intensive process comprising the following prior art processes:
1) Extruding an aluminum bar conforming to the general profile of the finished backing bar. An extrusion process, however, cannot yield the precision required for the part, particularly in respect to the straightness of the bar along its long dimension.
2) Machining each bar to enable the bar to be mounted to a grinding fixture and to machine holes at each end required for mounting and positioning of the finished backer bars adjacent to belt 10 within the printing system. The shape of prior art backer bars after machining is shown as bar 100 in FIG. 1. Significantly, although the rounded radius side 111 is the only side in contact with the moving imaging web in the final application, prior art processes require that both the radius surface 111 and at least one other surface be machined to great accuracy. As shown in FIG. 2, the reason is that at least one surface 112 (usually the bottom) other than the radius must be machined precisely in order that the unground raw backer bar be mounted with sufficient precision within a grinding fixture that will shape the final radius surface. If the bottom is not precisely straight, then the top radius surface will not be straight either. Since each backer bar is machined in its xe2x80x9cfree statexe2x80x9d, the costs and difficulty of this precision machining process are very significant.
3) Mounting each machined bar into a grinding fixture 113, as shown in FIG. 2. The prior art mounting fixture typically mounts 10 or more backer bars, depending upon the desired top radius.
4) Cylindrical grinding. Once the machined backer bars are mounted into grinding fixture 113, fixture 113 is placed in a cylindrical grinding apparatus comprising cylindrical grinding wheel 115 for grinding the top radius 111 of all bars mounted within the fixture to the precise radius curvature required. As noted above, straightness of the bar is largely determined by the straightness of the bottom surface since this bottom surface 112 determines the straightness of the backer bar within mounting fixture 113. The cylindrical grinding operation yields a precision-straight top surface of uniform radius dimension from the center of the mounting fixture.
5) Finishing the surface of the backer bars while placed within in the cylindrical grinder apparatus. Such finishing operation may require the additional use of various grades of grinding wheels 115 to achieve the required surface finish.
6) Anodizing the ground and finished backer bars.
The above prior art process is time consuming, labor intensive, and requires precision machining on at least two surfaces plus precision grinding. The end result is an expensive process with many opportunities yielding a significant failure rate. It would be advantageous to create precision backer bars having in a process requiring less machining and with higher yields.
One aspect of the present invention includes a process for manufacturing precision web guide members, comprising: (a) extruding a tube having a tubular body, a length dimension, an outside diameter, and an inside surface, said inside surface having radial cavities extending along the length dimension from the inside surface partially through the tubular body; (b) turning the tube to decrease the outside diameter; and (c) sizing the tube to a desired length.
Another aspect of the present invention includes a precision partially cylindrical web guide member for guiding a moving web member in an apparatus within which the web is moved, said web guide member comprising: a top surface for contacting the web comprising the outside surface of an arc segment of a cylindrical tube; and a bottom surface comprising the inside surface of the arc segment of the cylindrical tube.
Yet another aspect of the present invention includes an electrophotographic imaging system, comprising: (a) a partially cylindrical web guide member for guiding a moving web, said web guide member comprising: a top surface for contacting the web comprising the outside surface of an arc segment of a cylindrical tube; and a bottom surface comprising the inside surface of the arc segment of the cylindrical tube; and (b) a fixture for mounting the web guide member within the electrophotographic imaging system.